Add models to represent "Collections" (#36977)

db/migrate/20251118115657_create_collections.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class CreateCollections < ActiveRecord::Migration[8.0]
+  def change
+    create_table :collections do |t|
+      t.references :account, null: false, foreign_key: true
+      t.string :name, null: false
+      t.text :description, null: false
+      t.string :uri
+      t.boolean :local, null: false # rubocop:disable Rails/ThreeStateBooleanColumn
+      t.boolean :sensitive, null: false # rubocop:disable Rails/ThreeStateBooleanColumn
+      t.boolean :discoverable, null: false # rubocop:disable Rails/ThreeStateBooleanColumn
+      t.references :tag, foreign_key: true
+      t.integer :original_number_of_items
+
+      t.timestamps
+    end
+  end
+end

db/migrate/20251119093332_create_collection_items.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class CreateCollectionItems < ActiveRecord::Migration[8.0]
+  def change
+    create_table :collection_items do |t|
+      t.references :collection, null: false, foreign_key: { on_delete: :cascade }
+      t.references :account, foreign_key: true
+      t.integer :position, null: false, default: 1
+      t.string :object_uri, index: { unique: true, where: 'activity_uri IS NOT NULL' }
+      t.string :approval_uri, index: { unique: true, where: 'approval_uri IS NOT NULL' }
+      t.string :activity_uri
+      t.datetime :approval_last_verified_at
+      t.integer :state, null: false, default: 0
+
+      t.timestamps
+    end
+  end
+end